1. Field of the Invention
This invention relates generally to multiple pane sealed glazing units, and more particularly to multiple pane units having an insulating, flexible spacing and sealing assembly.
2. Description of the Prior Art
Insulating glass units generally consist of two or more parallel sheets of glass which are spaced apart from each other and which have the space between the panes sealed along the peripheries of the panes to enclose an air space between them. Spacer bars are placed along the periphery of the space between two panes. These spacer bars are typically long hollow perforated metal sections, usually made from an aluminum alloy and fabricated either in the form of an extrusion or by rolling from flat strip material. The hollow interior of the spacer contains a desiccant which is used to absorb any residual moisture that may be in the enclosed air and to soak up any additional moisture that may enter in the sealed unit over a period of time. The spacers are assembled into a rectangular frame typically using corner keys.
Units are constructed using either a single or dual seal. For single seal units, the structural, air and moisture vapour seal is combined in one seal. Sealant materials typically used with single seal design include either thermoplastic sealants such as butyl or thermosetting sealants such as polysulphide and polyurethane. In general, the thermosetting sealants are more permeable to moisture vapour than the thermoplastic sealants.
For dual seal units, there is an inner seal, as well as the main outer seal with the inner seal generally functioning as an additional moisture vapour seal. Typically, for dual seal units, the inner seal is a thermoplastic material such as polyisobutylene and a bead of the polyisobutylene is attached to the sides of the spacer adjacent to the glass sheets. The spacer frame is then placed between the panes and heat and/or pressure is applied to ensure that the polyisobutylene is compressed and fully wets out the surface of the glass. For the second outer seal, typically a thermosetting sealant such as silicone or polysulphide is used and is applied in the outward facing perimeter channel between the two glass sheets. Dual seal units are commonly used for automated production lines where the inner sealant is used as an adhesive holding the glass sheets in position on the conveyor line while the outer sealant cures.
To improve the thermal performance of multiple glazed sealed units increasingly units are being fabricated incorporating additional glazing sheets, where one or more of the parallel glazing sheets are being coated with a low-emissivity coating (low-e) to reduce radiation heat loss and the interconnected multiple airspaces are being filled with an inert gas such as argon to reduce conductive and convective heat loss.
Generally, conventional edge seal technology is inappropriate for high thermal performance units. There are a series of interrelated problems:
1. With conventional sealed units incorporating a conductive metal spacer, there is a thermal bridge between glazing layers and this can cause perimeter condensation and even ice build-up under extreme cold weather conditions.
2. With conventional sealed units, the percentage heat loss through the edge seal is about 5 percent of the overall heat loss through the window. For high thermal performance units incorporating conventional edge seal technology, the percentage heat loss is increased to 15 percent or more.
3. Low-e coatings intercept part of the solar spectrum causing the coated glazing to heat up. On cold, sunny days, the centre of the coated glazing can heat up and expand, but the expansion of the centre glass is constrained by the cold perimeter glass edge, creating stress in the glass sheet. Under extreme cold weather conditions, this thermal stress is sufficient to cause glass breakage.
4. Where low-e coatings are located on the inner glazing layers of multiple glazed units, the temperature within the airspaces of the sealed unit can be above 60.degree. C. Because of these high temperatures, there are larger pressure fluctuations within the sealed unit, and these larger pressure fluctuations result in increased movement and bowing of the glass sheets which in turn results in increased glass and sealant stress.
5. With single seal, multiple glazed units incorporating an outer thermoplastic sealant, there can be seal failure and loss of structural integrity due to the more extreme temperatures within the sealed unit.
6. With improved high thermal performance glazing, the temperature difference between the inner and outer glazing is increased. The outer glazing may be -30.degree. C. while the inner glazing is +16.degree. C. As a result of this increased temperature difference, there is increased differential expansion between the inner and outer glazing sheets which in turn results in increased sealant stress.
7. If there is any condensation within the sealed unit due to partial failure of the edge seal, the high performance silver-based, low-e coatings, will rapidly oxidize turning white and opaque.
8. Sealants such as polyurethane and silicone are comparitively permeable to gases such as argon and over time there is a gradual loss of the low-conductive gas resulting in reduced thermal performance.
9. Low-e coatings, particularly solar control low-e coatings, intercept ultra-violet (UV) radiation and prevent the damaging UV radiation from entering the building interior. As a result, where low-e coatings are located on the interior or centre glazing sheets, there is a build-up of ultra-violet radiation within the sealed unit. Plastic materials located within the sealed unit can be degraded by exposure to these higher levels of UV radiation.
Although these problems are more critical for high thermal performance glazing, the same problems also effect to some degree the performance of the edge seal of conventional sealed double glazing units.
In the past, various efforts have been made in the prior art to use non-metallic materials for the spacer assembly.
U.S. Pat. No. 49,167 issued to Stetson describes the fabrication of multiple pane sealed units using wood or string as the inner spacer and putty as the outer sealant.
U.S. Pat. No. 2,340,469 issued to Hall describes the use of a thermoplastic spacer in combination with a metal foil vapour barrier and where the solid rigid plastic is adhered directly to the glazing sheets and no outer sealant is used to seal the unit.
U.K. Pat. No. 868,885 issued to Midland Silicones Limited describes the use of silicone elastomeric spacers adhered to the glazing sheets by a curable silicone adhesive and where again no outer sealant is used to seal the unit.
U.S. Pat. No. 3,531,346 issued to Jameson describes how a compressible rubber seal can be used to simplify the construction of insulted glazing units for aircraft and space vehicles. The compressible seal reduces the need for manufacturing tolerance and prevents the liquid resin from leaking or smearing while the cast liquid resin cures to a hard material.
The common deficiency of the four spacing and sealing assemblies described above is that because the glazing units do not incorporate desiccant, over time, moisture vapour will build-up in the sealed unit causing condensation within the glazing unit which will gradually result in the formation of a white scum on the inner glazing faces due to leaching of salts from the glass.
U.S. Pat. No. 3,758,996 issued to Bowser describes the addition of desiccant material as a fill to a flexible but solid plastic spacer. The plastic spacer is backed by a layer of moisture resistant sealant typically thermoplastic butyl which extends across the spacer from the peripheral edge of one sheet to the peripheral edge of the other. The plastic spacer may be adhered to the glazing sheets with a rubber adhesive although polyisobutylene is typically used. The main drawbacks of this type of spacing and sealing assembly is that the process is slow, messy and complex. A further limitation is that this type of edge seal assembly can also only be used for double glazing.
U.S. Pat. No. 3,935,683 issued to Derner et al describes the use of a rigid plastic foam spacer. The rigid moisture permeable foam inner spacer which does not contain desiccant is used in combination with an outer spacer containing desiccant material within a solid profile. Again, the main drawback of this type of spacing and sealing assembly is the complexity of the assembly process for multiple glazed sealed units.
U.S. Pat. Nos. 4,226,063 and 4,205,104 issued to Chenel describes the use of a flexible spacing and sealing assembly comprising silicone as the outer sealant and desiccant-filled butyl sealant as the inner spacer which is extruded directly around the perimeter edge of the glass sheet.
In U.S. Pat. No. 4,622,249 issued to Bowser, the two materials are reversed and butyl is the outer sealant and desiccant filled silicone sealant is the inner spacer. The main drawback of both of these approaches is that very complex production equipment is required to fabricate the sealed units and that because of the complexity of the production process, the approach is effectively limited to only double glazed units.
As well as substituting non-metallic materials for the spacer assembly efforts have also been made in the prior art to develop simpler methods for manufacturing high performance glazing units.
U.S. Pat. No. 4,335,166 issued to Lizardo et al describes a method of manufacturing a sealed glazed unit incorporating a heat shrinkable plastic film, located between two outer glass sheets and which is typically surface coated with a low-e coating. A critical requirement is that to prevent wrinkles being formed at the corners following heat shrinking of the plastic film, the film must be held very rigidly in position. Typically, steel spacers are used in preference to aluminum because steel spacers are more rigid than aluminum. Although it is claimed by Lizardo et al that rigid plastic spacers could be used, it has been shown in practice that conventional solid plastic spacers are unsuitable because the spacers are not sufficiently stiff and rigid for this application.
U.S. Pat. No. 4,563,843 issued to Grether et al describes a method of manufacturing a thick airspace quad glazed unit. To achieve high thermal performance, the window incorporates multiple air spaces and two or more low-e coatings. To avoid the problem of pressure build-up within the thick airspace sealed unit, the unit is allowed to breath and a large quantity of desiccant material is used to ensure that moisture vapour is removed from the air entering the glazing unit.
One drawback with this design is the inconvenience and cost of occasionally replacing the desiccant material to ensure that no moisture vapour enters the glazing unit to degrade the low-e coatings. A second drawback is that because the unit breathes, it is impossible to incorporate low-conductive inert gas within the glazing unit. As a result and despite the complexity of the construction of the glazing unit, the thermal performance of the quad glazing unit is limited to only about RSI 1.4 (centre glazing).